The latest bid for freedom was made by chimps who used a branch as a makeshift ladder and scaled high walls surrounding their pen on Saturday.

Visitors described seeing one of the escapees emerge from the bushes on to a path while others were sitting on top of their enclosure wall.

In footage posted on social media, a child can be heard exclaiming: “Don’t escape, you bad little gorilla.”

Zookeeper Alyn Cairns said trees in the enclosure had been weakened by the storms, allowing the chimps to break them and use them as a ladder to escape.

He told the BBC: “They’re intelligent primates and know they’re not supposed to be out of their enclosure, so got back in themselves.”

Danielle Monaghan, who was at the zoo with her two children, partner and his young nieces, expressed concern about safety.

“I was petrified, obviously, having the kids, and I tried not to show fear but inside I was a bit like: what happens if it attacks us or tries to take the kids or runs over?” she told the BBC.

“But we just had to stay calm. It may have been a different story if it had been aggressive but it absolutely wasn’t. It made us feel at ease. We just walked past it and it was absolutely grand.”

She said they were in disbelief when they saw one of the chimpanzees start to climb out of its enclosure and ended up a foot away when they walked over to take a closer look.

A spokesperson for Belfast city council, which runs the zoo, said one chimpanzee left its enclosure for a short time. “Zookeepers were present as the chimpanzee quickly returned from an adjacent wall to the rest of the group inside the enclosure,” it said.